Generally, an ultrasound diagnostic system projects ultrasound signals from a surface of a target object toward a desired part within the target object. This is to obtain an ultrasound image of a soft tissue or blood flow by non-invasive means through using information of ultrasound echo signals from the target object. Compared to other medical imaging systems (e.g., X-ray diagnostic system, X-ray CT scanner, MRI and nuclear medicine diagnostic system), the ultrasound diagnostic system is advantageous since it is small in size and fairly inexpensive. Further, the ultrasound diagnostic system is capable of providing real-time display and is highly safe without any dangerous side effects such as exposure to X-rays, etc. Thus, it is extensively utilized for diagnosing the heart, abdomen and urinary organs, as well as being widely applied in the fields of obstetrics, gynecology, etc.
The ultrasound diagnostic system forms ultrasound images of various modes (e.g., B-mode, M-mode, etc.) based on the ultrasound echo signals reflected from the target object. Also, the ultrasound diagnostic system can provide a color flow image, which indicates the velocities of a moving target object and scatters. The ultrasound diagnostic system displays the velocity and direction of blood flowing within a moving object (e.g., heart, blood vessel or the like) with various colors based on the Doppler shift of an ultrasound signal. For example, the conventional ultrasound diagnostic system indicates the blood flowing toward the transducer of the probe with a red color, while indicating the blood flowing backward from the transducer of the probe with a blue color. Furthermore, the conventional diagnostic system indicates a rapidly flowing blood with a light color, while indicating a slowly flowing blood with a dark color.
Since the conventional diagnostic system displays the color Doppler image, which indicates the velocities of the moving target object and the scatters, on a 2-dimensional level, there is a problem in that a person unskilled in the conventional diagnostic system cannot accurately analyze the 2-dimensional color Doppler image.
In order to overcome the above problem, the conventional ultrasound diagnostic system superposes a plurality of 2-dimensional ultrasound images to provide a 3-dimensional color Doppler image. This is so that the above unskilled person can easily examine the target object through the displayed 3-dimensional color Doppler image. However, if the 2-dimensional color Doppler images indicating different blood flows are superposed, then the colors indicating the blood flows are displayed while the images are superposed. Therefore, there is a problem in that the conventional ultrasound diagnostic system cannot provide accurate information of the blood flows.